Nanu is a new ad-supported app for Android that allows its users to call each other for free even if they use low-bandwidth 2G networks, while it also allows some calls to landlines and mobile numbers for no cost.

Existing apps have two major problems, according to Nanu. “First, they struggle in congested 3G networks and just don’t work in 2G. Second, you can only call app-to-app for free. App-to-non app calls such as calls to landlines and mobile phones cost money,” the founders of Singapore-based Nanu said.

Nanu-to-Nanu calls are free, excluding the cost of the data connection. The calls consume about 100 kilobytes of data per minute, so when using the app on a 2G, 3G or 4G network, users may still have to pay data charges to their carrier.

The first million users will also get 15 minutes of Nanu to non-Nanu calls for free. These minutes can be used to call landlines in 41 countries including the U.S., U.K., France, Germany, Australia and New Zealand. In addition, free minutes can be used to call mobile phones in the U.S., Germany, India and six other countries, according to Nanu’s site.

Nanu makes its money by playing ads over the ringtones while users are waiting for calls to connect. “As more and more people use Nanu, we will be able to offer more and more free Nanu to non-Nanu calls,” the Nanu team said.

While only available for Android at the moment, the app should appear on iOS and Windows later this year and other operating systems shortly after.

Mobile phone services that allow users to make free calls or send text messages in exchange for receiving targeted advertising have often folded after a few years. In Europe for instance Blyk offered its users free calls and text messaging for a few years. Its U.K. business closed in 2009 while in the Netherlands it switched to a paid rather than ad-supported business model.

More recently, British mobile firm Ovivo closed its ad-subsidised services without a warning in March for unspecified reasons. The service displayed ads in customers’ mobile browsers every ten minutes. The deal included calling, text and data packages for a £20 up-front fee, £15 of which would be turned into credit balance.

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